Accept Encoding Header
Accept-Encoding – HTTP – MDN Web Docs
The Accept-Encoding request HTTP header indicates the content encoding (usually a compression algorithm) that the client can understand. The server uses content negotiation to select one of the proposal and informs the client of that choice with the Content-Encoding response header.
Even if both the client and the server support the same compression algorithms, the server may choose not to compress the body of a response if the identity value is also acceptable. Two common cases lead to this:
The data to be sent is already compressed, therefore a second compression will not reduce the transmitted data size. This is true for pre-compressed image formats (JPEG, for instance);
The server is overloaded and cannot allocate computing resources to perform the compression. For example, Microsoft recommends not to compress if a server uses more than 80% of its computational power.
As long as the identity;q=0 or *;q=0 directives do not explicitly forbid the identity value that means no encoding, the server must never return a 406 Not Acceptable error.
Note:
An IANA registry maintains a complete list of official content encodings.
Two other content encodings, namely bzip and bzip2, are sometimes used, These non-standard encodings implement the algorithm that these two UNIX programs use. Note that bzip was discontinued due to patent licensing issues.
Header type
Request header
Forbidden header name
yes
SyntaxAccept-Encoding: gzip
Accept-Encoding: compress
Accept-Encoding: deflate
Accept-Encoding: br
Accept-Encoding: identity
Accept-Encoding: *
// Multiple algorithms, weighted with the quality value syntax:
Accept-Encoding: deflate, gzip;q=1. 0, *;q=0. 5
Directives
gzip
A compression format that uses the Lempel-Ziv coding (LZ77) with a 32-bit CRC.
compress
A compression format that uses the Lempel-Ziv-Welch (LZW) algorithm.
deflate
A compression format that uses the zlib structure with the deflate compression algorithm.
br
A compression format that uses the Brotli algorithm.
identity
Indicates the identity function (that is, without modification or compression). This value is always considered as acceptable, even if omitted.
*
Matches any content encoding not already listed in the header. This is the default value if the header is not present. This directive does not suggest that any algorithm is supported but indicates that no preference is expressed. ;q= (qvalues weighting)
Any value is placed in an order of preference expressed using a relative quality value called weight.
ExamplesAccept-Encoding: gzip
Accept-Encoding: gzip, compress, br
Accept-Encoding: br;q=1. 0, gzip;q=0. 8, *;q=0. 1
SpecificationsSpecificationHypertext Transfer Protocol (HTTP/1. 1): Semantics and Content (HTTP/1. 1)# compatibilityBCD tables only load in the browserSee also
HTTP content negotiation
A header with the result of the content negotiation: Content-Encoding
Other similar headers: TE, Accept, Accept-Language
Accept-Encoding – HTTP – MDN Web Docs
The Accept-Encoding request HTTP header indicates the content encoding (usually a compression algorithm) that the client can understand. The server uses content negotiation to select one of the proposal and informs the client of that choice with the Content-Encoding response header.
Even if both the client and the server support the same compression algorithms, the server may choose not to compress the body of a response if the identity value is also acceptable. Two common cases lead to this:
The data to be sent is already compressed, therefore a second compression will not reduce the transmitted data size. This is true for pre-compressed image formats (JPEG, for instance);
The server is overloaded and cannot allocate computing resources to perform the compression. For example, Microsoft recommends not to compress if a server uses more than 80% of its computational power.
As long as the identity;q=0 or *;q=0 directives do not explicitly forbid the identity value that means no encoding, the server must never return a 406 Not Acceptable error.
Note:
An IANA registry maintains a complete list of official content encodings.
Two other content encodings, namely bzip and bzip2, are sometimes used, These non-standard encodings implement the algorithm that these two UNIX programs use. Note that bzip was discontinued due to patent licensing issues.
Header type
Request header
Forbidden header name
yes
SyntaxAccept-Encoding: gzip
Accept-Encoding: compress
Accept-Encoding: deflate
Accept-Encoding: br
Accept-Encoding: identity
Accept-Encoding: *
// Multiple algorithms, weighted with the quality value syntax:
Accept-Encoding: deflate, gzip;q=1. 0, *;q=0. 5
Directives
gzip
A compression format that uses the Lempel-Ziv coding (LZ77) with a 32-bit CRC.
compress
A compression format that uses the Lempel-Ziv-Welch (LZW) algorithm.
deflate
A compression format that uses the zlib structure with the deflate compression algorithm.
br
A compression format that uses the Brotli algorithm.
identity
Indicates the identity function (that is, without modification or compression). This value is always considered as acceptable, even if omitted.
*
Matches any content encoding not already listed in the header. This is the default value if the header is not present. This directive does not suggest that any algorithm is supported but indicates that no preference is expressed. ;q= (qvalues weighting)
Any value is placed in an order of preference expressed using a relative quality value called weight.
ExamplesAccept-Encoding: gzip
Accept-Encoding: gzip, compress, br
Accept-Encoding: br;q=1. 0, gzip;q=0. 8, *;q=0. 1
SpecificationsSpecificationHypertext Transfer Protocol (HTTP/1. 1): Semantics and Content (HTTP/1. 1)# compatibilityBCD tables only load in the browserSee also
HTTP content negotiation
A header with the result of the content negotiation: Content-Encoding
Other similar headers: TE, Accept, Accept-Language
HTTP headers | Accept-Encoding – GeeksforGeeks
The HTTP headers Accepts-Encoding is usually a comparison algorithm of request header. All the HTTP client used to tell the server which encoding or encoding it supports. Then the server will respond in any of the supporting encoding formats. The server selects any one of the proposals, uses it and informs the client of its choice with the Content-Encoding response gzip | compress | deflate | br| identity| *Note: Multiple algorithm are also can be ives:gzip: It is a compression format using the Lempel-Ziv coding (LZ77), with a 32-bit mpress: It is a compression format using the Lempel-Ziv-Welch (LZW) flate: It is a compression format using the zlib structure, with the deflate compression It is a compression format using the Brotli entity: This directive Indicates the identity function which is always acceptable. *: This directive matches any content encoding which can be listed in the header or not. It is the default can check how good your Accept-Encoding and Content-Encoding is working on this site. Example:Accept-Encoding: gzip, deflate, brAccept-Encoding: br;q=1. 0, gzip;q=0. 6, *;q=0. 1To check this Accept-Encoding in action go to Inspect Element -> Network check the request header for Accept-Encoding like below, Accept-Encoding is highlighted you can pported Browsers: The browsers compatible with HTTP headers Accept-Encoding are listed below:Google ChromeInternet ExplorerFirefoxSafariOpera
Frequently Asked Questions about accept encoding header
What does accept-Encoding header do?
The Accept-Encoding request HTTP header advertises which content encoding, usually a compression algorithm, the client is able to understand. Using content negotiation, the server selects one of the proposals, uses it and informs the client of its choice with the Content-Encoding response header.Aug 13, 2021
How do I set the Encoding header?
To check this Accept-Encoding in action go to Inspect Element -> Network check the request header for Accept-Encoding like below, Accept-Encoding is highlighted you can see.Oct 23, 2019
What is content Encoding header?
The Content-Encoding representation header lists any encodings that have been applied to the representation (message payload), and in what order. … Content encoding is mainly used to compress the message data without losing information about the origin media type.Aug 13, 2021
